I don't know anything about the specific message you saw nor the specific attack you just received.... but there have not been any viable, active, Mac viruses in the wild for many many years. Moreover, no one on any of the many Mac websites has reported any such thing for many years. I would say you are 100% safe and did the right thing by simply closing that window. Recently, there have been quite a few different web-based attacks in which particular sites send you bogus web pages that can, at least temporarily, corrupt your web browser. Understand that they attack your browser rather than the computer itself. These can always (?) be cleared up by "resetting" the browser or getting rid of prefs files and cookies. They're annoying but not serious. I will let the other club members weigh in on this...

I experienced the same message awhile back. Like you, I just closed the window and have continued using the computer with no problems. I think it is a bogus (scam) message and if you follow the link it may deposit a piece of malware in your computer. Everything I have read about these messages says not to go there. I have wondered if you followed the link whether it would work on a MAC. I think they are designed for PC's. I am not brave enough to try it.